Lasers are employed in a number of applications, including both commercial and military applications. In general, lasers provide a highly precise mechanism to communicate information (e.g., control signals or targeting information) from one point to another. The distance between the points may be a short distance (e.g., closed box applications) or a great distance (e.g., laser guided targeting applications). Optics are used in conjunction with the laser, so as to control the path which the laser beam follows. Thus, precision aiming of the laser beam is enabled.
In many applications, controlling the laser beam so that it remains on its intended path is not trivial, particularly those applications where the laser system is subjected to harsh thermal and dynamic environments. The slightest deviation from the desired beam path can render a laser system unreliable for its intended purpose. The optics must therefore operate to continuously adjust to ensure beam accuracy. In addition, where the laser beam is switchable between two or more paths, the switching scheme must be highly repeatable (e.g., within one milliradian) so as to prevent inconsistencies associated with the paths.
There are a number of existing mechanisms that enable highly repeatable laser switching schemes, such as stepper driven or motion controlled brushless DC driven single axis stages, over-center toggle mechanisms driven by snap action solenoids, low backlash driven mechanisms using highly accurate feedback from a sensor such as an optical encoder or Eddy current sensor, or a single axis linear stepper motor for directly positioning the optic on a moving platen (armature). Each of these mechanisms is associated with a number of disadvantages.
For example, stepper motors and motion controlled brushless DC motors require considerable electronic and mechanical hardware to control motion. Such motor based schemes are typically appropriate when controlled contouring motion is required, but are overkill for point to point applications where low cost, small size, and low complexity are required. In addition, these methods allow sensing of the motor axis motion, which when performed, still requires a close to zero backlash connection between the motor and optic, thereby increasing cost and complexity.
Since small solenoids cannot be continuously energized without direct cooling, solenoid driven mechanisms used in small systems in harsh environments usually involve push-pull arrangements requiring two coils, coupled to an over-center toggle mechanism. Alternatively, there are two solenoids, with one for actuating and the other for locking the device. This is often acceptable when the device being moved is of extremely low mass. However, if the object has a relatively large mass, then the solenoid driven mechanism must be of sufficient size to accomplish placement and holding. Furthermore, such a solenoid driven mechanism employs “snap action” by definition. Oftentimes, however, no dashpot or other damping mechanism is allowed due to cleanliness requirements in the optical compartment.
Optical encoders are typically big and expensive. In addition, an appropriate encoder for closed box applications associated with high mass devices would be linear, and would sense the actual optic (or its mount) position. In harsh environments, maintaining optic/mount in a precise position may be difficult or untenable. An Eddy current sensor would sufficiently sense final position of the optic or mount, but such sensors are extremely expensive. Moreover, a scheme would have to be devised to hold the position of the optic in a harsh thermal and dynamic environment. Linear steppers are also expensive, and require separate motion control apparatus.
What is needed, therefore, are low cost and complexity techniques for causing a laser beam, to switch from one path to another, where each path has high dimensional stability in a harsh thermal and dynamic environment.